The previous answers are fairly spot on. The truth is, most people are intimidated by the success of others. I believe it has more to do with self insecurities and the understanding that these individuals need to themselves make life changes but have an unwillingness to do so. When someone is a smoker, drinker, heavy eater, non-exerciser, they want to be with others who share those same qualities as it often makes them feel better.
For the individual looking to change those bad habits, I believe it’s important to find similar people who will be advocates for their behavioral changes. This doesn’t mean they have to distance themselves from friends, but at least in the immediate future find a great support group who will be encouraging and help you along the way.